1. Field of the Invention
The present invention relates to a method of processing photosensitive glass by etching.
2. Description of the Prior Art
There has heretofore been a method of processing photosensitive glass by etching to form fine shapes, for example, ink-jet printer heads. This method includes the steps of exposing a desired portion of photosensitive glass by irradiation with an ultraviolet lamp (exposure step), crystallizing the exposed portion by heating the photosensitive glass to a temperature in the range of 500.degree. C. to 700.degree. C. (heat development step), and removing the crystallized exposed portion by dissolving it in an etching liquid, i.e., hydrofluoric acid solution, (etching step). As the ultraviolet lamp, for example, a high-pressure mercury lamp is employed.
Meantime, there is a process where only one side of photosensitive glass is etched to form groove portions or the like. In this process, the reverse side of the photosensitive glass that is not desired to be etched is covered with etching protecting tape or the like before the etching step in order to protect it from the etching liquid, or the reverse side of the photosensitive glass is kept away from the etching liquid by using an etching jig.
In the conventional method, the control of the etch depth of groove portions or the like, which are cut in photosensitive glass by etching crystallized exposed portions formed on the photosensitive glass, is effected on the basis of etching conditions, i.e., etching time, the temperature and concentration of the etching liquid, etc. However, the etch rate of the crystallized exposed portions depends not only on such etching conditions but also on other factors, for example, exposure intensity, heat development conditions, etc. Further, the etch rate varies according to various factors such as fatigue of the etching liquid, contamination of the etching liquid with the crystallized portions of the photosensitive glass which are dissolved by etching, and the way in which the crystallized portions are exposed to the etching liquid. Therefore, the control of the etch depth has heretofore been extremely difficult.
The prior art also suffers from the problem that the etched surface of the crystallized exposed portion has a large surface roughness. In ink-jet printer head application, if the path of ink is formed by a surface having a large surface roughness, air bubbles mixed in the ink are likely to stagnate, producing an adverse effect on the ink injection characteristics. In micro-machining application, the prior art suffers from the problem that a mechanical drive part cannot move smoothly because of large friction.
Further, in the case of single-side etching, it takes time and labor to cover the photosensitive glass with protecting tape before the etching process and strip the tape thereafter. In addition, the photosensitive glass substrate may be damaged when the tape is stripped therefrom. The use of a jig for the etching process involves the problems that such an etching jig is costly, and that since force is applied to the photosensitive glass when attached to the jig, the glass is readily broken during the etching process, which invites a lowering in the yield.